In addition to mental retardation, individuals with Down syndrome (DS) universally develop the neuropathological hallmarks of Alzheimer's Disease (AD) in early adulthood. A mouse model of DS and AD, the Ts65Dn mouse, exhibits key features of these disorders, including early degeneration of cholinergic basal forebrain (CBF) neurons and impairments in the cognitive functions dependent on these neurons and their projection systems, namely, explicit memory and attentional function. We recently completed a study to test the hypothesis that supplementation of the maternal diet with excess choline during pregnancy and lactation would lessen the attentional dysfunction seen in Ts65Dn mice. This study revealed a remarkable benefit of perinatal choline supplementation for the Ts65Dn mice: They performed significantly better than unsupplemented Ts65Dn mice on a series of visual attention tasks, and in fact, on some tasks, did not differ from the disomic (2N) controls. For one task, the 2N mice also benefited from the increased maternal choline intake. The studies proposed herein are designed to elaborate upon these observations with three Specific Aims: (1) To test the hypothesis that the benefit of perinatal choline supplementation in Ts65Dn and 2N mice extends to functions dependent on the cholinergic septo-hippocampal system; (2) To test the hypothesis that the cognitive benefit produced by early choline supplementation in Ts65Dn and 2N mice is mediated by increased number, size, and/or phenotypic expression of cholinergic neurons in specific basal forebrain nuclei (medial septal nucleus and nucleus basalis) and/or their projection systems, using unbiased stereologic cell counting techniques. Quantitative morphometry will be correlated with measures of memory and attention from these same animals to assess the functional significance of any observed changes; (3) To test the hypothesis that improved cognitive functioning in Ts65Dn and 2N mice is mediated by alterations in the nerve growth factor (NGF) family of neurotrophins and its cognate receptors in CBF target regions (frontal cortex and hippocampus). Levels of these neurotrophins and receptors will be measured using immunoblotting and correlated with measures of memory and attention from these same subjects to establish structure-function relationships. The evidence for lifelong cognitive and neural benefits of perinatal choline supplementation in normal rodents and this mouse model of DS/AD raises the possibility that recommendations for choline intake, currently based on preventing liver damage, may need to be re-evaluated, and that higher levels may be needed for optimal brain function. These recent findings suggest that perinatal choline supplementation might significantly reduce the cognitive dysfunction seen in DS as well as reduce the risk of AD and age-related cognitive decline in the population at large. The proposed research is designed to increase our understanding of these effects and begin to elucidate the underlying neural mechanisms subserving these behavioral changes, information that is needed to inform these potential changes in recommendations for choline intake during pregnancy, lactation, and early development.